Cursor related const's are only compatible with LoadCursorW

[mdeforge]

Summary

Cursor related const's such as IDC_ARROW in Windows\Win32\UI\WindowsAndMessaging\mod.rs are only compatible with the wide LoadCursorW function and not with the non-wide LoadCursorA function.

This is due to the const's being declared as PCWSTR's and not PCSTR's. However, switching would break the wide version of the function.

I'm new to Rust, so I may be missing an easy solution here. However, I think this use case should be supported, no?

Error:

error[E0277]: the trait bound `PCWSTR: CanInto<PCSTR>` is not satisfied
    --> src\main.rs:5:49
     |
5    |         let version = LoadCursorA(HINSTANCE(0), IDC_ARROW);
     |                       -----------               ^^^^^^^^^ the trait `CanInto<PCSTR>` is not implemented for `PCWSTR`
     |                       |
     |                       required by a bound introduced by this call
     |
     = help: the following other types implement trait `CanInto<T>`:
               <IAgileObject as CanInto<IUnknown>>
               <IAgileReference as CanInto<IUnknown>>
               <IErrorInfo as CanInto<IUnknown>>
               <ILanguageExceptionErrorInfo as CanInto<IUnknown>>
               <ILanguageExceptionErrorInfo2 as CanInto<IUnknown>>
               <ILanguageExceptionErrorInfo2 as CanInto<ILanguageExceptionErrorInfo>>
               <IPropertyValue as CanInto<IUnknown>>
               <IPropertyValue as CanInto<IInspectable>>
             and 12 others
     = note: required for `PCWSTR` to implement `IntoParam<PCSTR, CopyType>`
note: required by a bound in `WindowsAndMessaging::LoadCursorA`
    --> C:\Users\Michael\.cargo\registry\src\index.crates.io-6f17d22bba15001f\windows-0.52.0\src\Windows\Win32\UI\WindowsAndMessaging\mod.rs:2260:9
     |
2257 | pub unsafe fn LoadCursorA<P0, P1>(hinstance: P0, lpcursorname: P1) -> ::windows_core::Result<HCURSOR>
     |               ----------- required by a bound in this function
...
2260 |     P1: ::windows_core::IntoParam<::windows_core::PCSTR>,
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `LoadCursorA`

Crate manifest

[package]
name = "CursorIssue"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies.windows]
version = "0.52"
features = [
    "Win32_Foundation",
    "Win32_UI_WindowsAndMessaging"
]

Crate code

use windows::Win32::{Foundation::*, UI::WindowsAndMessaging::*};

fn main() {
    unsafe {
        let version = LoadCursorA(HINSTANCE(0), IDC_ARROW); // Does not work
        let wide_version = LoadCursorW(HINSTANCE(0), IDC_ARROW); // Works
    }
}

[riverar]

This is an upstream metadata issue; will transfer there for discussion/resolution.

In the short term, you can use windows::core::PCSTR(32512u16 as _) as a workaround.

[mikebattista]

What's the proposed metadata change here?

[riverar]

Not sure yet, do we have any other examples of how we've incorporated constants into metadata that change (in type), depending on the value of _UNICODE?

[mikebattista]

I don't believe so. We build for UNICODE. In cases where this is an explicit _A variant of the constant, we decorate that variant with the NativeEncoding(ansi) attribute, but I don't recall supporting conditional values for the same constant.

[riverar]

@mikebattista Hm, looks like we may have to explicitly add both variants with _A/_W suffixes. Still thinking though. 💭